Radar array phase shifter verification

ABSTRACT

An improved circuit configuration is disclosed for calibrating and/or verifying the operation of phase shifters in a phased array radar system. In one illustrative embodiment, a method includes: (i) programming a set of phase shifters to convert a radio frequency signal into a set of channel signals; (ii) splitting off a monitor signal from each channel signal while coupling the set of channel signals to a set of antenna feeds; and (iii) while taking the monitor signals in pairs associated with adjacent channels, measuring a relative phase between each pair of monitor signals.

BACKGROUND

In the quest for ever-safer and more convenient transportation options,many car manufacturers are developing self-driving cars which require animpressive number and variety of sensors. Among the contemplated sensingtechnologies are multi-input, multi-output radar systems to monitor thedistances between the car and any vehicles or obstacles along the travelpath. Such systems may employ beam-steering techniques to improve theirmeasurement range and resolution.

On the transmit side, beam-steering is often performed using a phasedarray, i.e., by supplying a transmit signal with different phase shiftsto each of multiple antennas, the beam direction being determined by thedifferences between the phase shifts. As the phase differences arevaried to steer the beam, it is desirable that the signal amplitudesremain the same. Device mismatch, even that due to temperature andaging, may cause distort the beam pattern and may even cause sidelobeformation. Such effects may shift the apparent direction of obstacles orcreate nulls that entirely “conceal” obstacles. Thus automotive radarsafety standards, or engineering design prudence alone, may dictate thatsome mechanism be included to calibrate and/or verify proper operationof the phase shifters. Existing mechanisms for this purpose may undulycompromise the cost or reliability of the automotive radar systems.

SUMMARY

The problems identified above may be addressed at least in part by animproved circuit configuration for calibrating and/or verifying theoperation of phase shifters in a phased array radar system. In oneillustrative embodiment, a method includes: (i) programming a set ofphase shifters to convert a radio frequency signal into a set of channelsignals; (ii) splitting off a monitor signal from each channel signalwhile coupling the set of channel signals to a set of antenna feeds; and(iii) while taking the monitor signals in pairs associated with adjacentchannels, measuring a relative phase between each pair of monitorsignals.

In another illustrative embodiment, a radar system includes: a signalgenerator that supplies a radio frequency signal; a set of programmablephase shifters that convert the radio frequency signal into a set ofchannel signals; and a set of couplers that couples the set of channelsignals to a set of antenna feeds, the couplers in said set providingmonitor signals. The system further includes one or more power combinersthat each combine a pair of monitor signals to produce a combinedsignal; and one or more power detectors that each convert a respectivecombined signal into a power level signal. A controller uses at leastone said power level signal to determine a relative phase between atleast one pair of channel signals in said set of channel signals.

In still another illustrative embodiment, a radar system includes: asignal generator that supplies a radio frequency signal; a set ofprogrammable phase shifters that convert the radio frequency signal intoa set of channel signals; and a set of couplers that couples the set ofchannel signals to a set of antenna feeds, the couplers in said setproviding monitor signals. One or more phase detectors are provided toeach determine a relative phase between monitor signals for a pair ofadjacent channels.

Each of the foregoing embodiments can be employed individually or inconjunction, and may include one or more of the following features inany suitable combination: 1. providing an error notification if one ofsaid relative phase measurements fails to match a difference inprogrammed phase shifts of the set of phase shifters. 2. acquiringsequential relative phase measurements over a range of phase settings ofphase shifters associated with even channels while maintaining a phasesetting of phase shifters associated with odd channels, and acquiringsequential relative phase measurements over a range of phase settings ofphase shifters associated with odd channels while maintaining a phasesetting of phase shifters associated with even channels. 3. providing anerror notification if a difference between sequential relative phasemeasurements fails to match a predetermined step size. 4. determining aphase setting offset for each pair based on the relative phasemeasurements. 5. said determining includes measuring the relative phaseover a range of phase setting differences for adjacent channels. 6. saidmeasuring includes: combining each pair of monitor signals to form acombined signal; and measuring a power of each combined signal. 7.disabling adjustable gain amplifiers associated with odd channels whilemeasuring the power of each combined signal; disabling adjustable gainamplifiers associated with even channels while measuring the power ofeach combined signal; and based on said power measurements, adjustinggains of the adjustable gain amplifiers to equalize the power of eachchannel signal in said set of channel signals. 8. the controller usesthe at least one power level signal to determine a phase setting offsetfor each pair. 9. the controller determines the phase setting offset by:measuring at least one power level signal over a range of phase settingdifferences for adjacent channels; and identifying a power level maximumor minimum that corresponds to the phase setting offset. 10. the one ormore power combiners are anti-phase combiners and the phase settingoffset corresponds to a power level minimum. 11. the one or more powercombiners are in-phase combiners and the phase setting offsetcorresponds to a power level maximum. 12. a set of adjustable gainamplifiers that amplify the set of channel signals provided to the setof couplers. 13. prior to determining the relative phase, the controlleradjusts gains of the adjustable gain amplifiers to equalize power ofeach channel signal in the set of channel signals. 14. prior toequalizing power, the controller disables the adjustable gain amplifiersassociated with odd channels while measuring the power of each combinedsignal; and disables the adjustable gain amplifiers associated with evenchannels while measuring the power of each combined signal. 15. acontroller that: acquires sequential relative phase measurements over arange of phase settings of phase shifters associated with even channelswhile maintaining a phase setting of phase shifters associated with oddchannels; acquires sequential relative phase measurements over a rangeof phase settings of phase shifters associated with odd channels whilemaintaining a phase setting of phase shifters associated with evenchannels; and provides an error notification if a difference betweensequential relative phase measurements fails to match a predeterminedstep size. 16. the one or more phase detectors comprises a pair of phasedetectors that determines a first relative phase between a centerchannel and a first adjacent channel, and a second relative phasebetween the center channel and a second adjacent channel, the systemfurther comprising a controller that computes a difference between thefirst and second relative phases. 17. the controller provides an errornotification if the difference fails to match an expected differencebased on phase settings of the phase shifters associated with the centerchannel, the first adjacent channel, and the second adjacent channel.18. the expected difference is (j+l−2k)Δθ_(s), with j, k, and lrepresenting phase settings of the first adjacent channel, the centerchannel, and the second adjacent channel, respectively, and Desrepresenting a predetermined step change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overhead view of an illustrative vehicle equipped withsensors.

FIG. 2 is a block diagram of an illustrative driver-assistance system.

FIG. 3 is a block diagram of an illustrative radar transceiver chip.

FIG. 4 is a block diagram of an illustrative phase shift transmit array.

FIG. 5 is a schematic of an illustrative phase detector.

FIG. 6 is a schematic of an illustrative calibration circuit.

FIG. 7 is a schematic of an illustrative verification circuit.

FIG. 8 is a schematic of another illustrative calibration circuit.

FIG. 9A is a graph of anti-phase combiner output vs. phase.

FIG. 9B is a graph of in-phase combiner output vs. phase.

FIG. 10A is a flow diagram of an illustrative verification method.

FIG. 10B is a flow diagram of an illustrative calibration method.

DETAILED DESCRIPTION

It should be understood that the following description and accompanyingdrawings are provided for explanatory purposes, not to limit thedisclosure. To the contrary, they provide the foundation for one ofordinary skill in the art to understand all modifications, equivalents,and alternatives falling within the scope of the claims.

FIG. 1 shows an illustrative vehicle 102 equipped with an array of radarantennas, including antennas 104 for short range sensing (e.g., for parkassist), antennas 106 for mid-range sensing (e.g., for monitoring stop &go traffic and cut-in events), antennas 108 for long range sensing(e.g., for adaptive cruise control and collision warning), each of whichmay be placed behind the front bumper cover. Antennas 110 for shortrange sensing (e.g., for back-up assist) and antennas 112 for mid rangesensing (e.g., for rear collision warning) may be placed behind the backbumper cover. Antennas 114 for short range sensing (e.g., for blind spotmonitoring and side obstacle detection) may be placed behind the carfenders. Each set of antennas may perform multiple-input multiple-output(MIMO) radar sensing. The type, number, and configuration of sensors inthe sensor arrangement for vehicles having driver-assist andself-driving features varies. The vehicle may employ the sensorarrangement for detecting and measuring distances/directions to objectsin the various detection zones to enable the vehicle to navigate whileavoiding other vehicles and obstacles.

FIG. 2 shows an electronic control unit (ECU) 202 coupled to the variousradar sensing front ends 204-206 as the center of a star topology. Ofcourse, other topologies including serial, parallel, and hierarchical(tree) topologies, are also suitable and contemplated for use inaccordance with the principles disclosed herein. The radar front endseach include a radio frequency (RF) transceiver which couples to some ofthe transmit and receive antennas 104-114 to transmit electromagneticwaves, receive reflections, and optionally to perform processing fordetermining a spatial relationship of the vehicle to its surroundings.(Such processing may alternatively be performed by the ECU 202.) Toprovide automated parking assistance, the ECU 202 may further connect toa set of actuators such as a turn-signal actuator 208, a steeringactuator 210, a braking actuator 212, and throttle actuator 214. ECU 202may further couple to a user-interactive interface 216 to accept userinput and provide a display of the various measurements and systemstatus.

Using the interface, sensors, and actuators, ECU 202 may provideautomated parking, assisted parking, lane-change assistance, obstacleand blind-spot detection, autonomous driving, and other desirablefeatures. In an automobile, the various sensor measurements are acquiredby one or more electronic control units (ECU), and may be used by theECU to determine the automobile's status. The ECU may further act on thestatus and incoming information to actuate various signaling and controltransducers to adjust and maintain the automobile's operation. Among theoperations that may be provided by the ECU are various driver-assistfeatures including automatic parking, lane following, automatic braking,and self-driving.

To gather the necessary measurements, the ECU may employ a MIMO radarsystem. Radar systems operate by emitting electromagnetic waves whichtravel outward from the transmit antenna before being reflected back toa receive antenna. The reflector can be any moderately reflective objectin the path of the emitted electromagnetic waves. By measuring thetravel time of the electromagnetic waves from the transmit antenna tothe reflector and back to the receive antenna, the radar system candetermine the distance to the reflector. If multiple transmit or receiveantennas are used, or if multiple measurements are made at differentpositions, the radar system can determine the direction to the reflectorand hence track the location of the reflector relative to the vehicle.With more sophisticated processing, multiple reflectors can be tracked.At least some radar systems employ array processing to “scan” adirectional beam of electromagnetic waves and construct an image of thevehicle's surroundings. Both pulsed and continuous-wave implementationsof radar systems can be implemented, though frequency modulatedcontinuous wave radar systems are generally preferred for accuracy.

FIG. 3 shows a block diagram of an illustrative transceiver chip 300 fora radar system. The chip 300 has antenna feeds or terminals coupled toan array of transmit antennas 301 and receive antennas 302. Adjustablegain amplifiers 303A-303D drive the transmit antennas 301 with amplifiedsignals from transmitter circuitry 304. Circuitry 304 generates acarrier signal within a programmable frequency band, using aprogrammable chirp rate and range. The signal generator may employ avoltage controlled oscillator with suitable frequency multipliers.Splitters and phase shifters derive the transmit signals for themultiple transmitters TX-1 through TX-4 to operate concurrently, andfurther provide a reference “local oscillator” signal to the receiversfor use in the down-conversion process. In the illustrated example, thetransceiver chip 300 includes 4 transmitters (TX-1 through TX-4) each ofwhich is fixedly coupled to a corresponding transmit antenna 301. Inalternative embodiments, multiple transmit antennas are selectablycoupled to each of the transmitters.

Chip 300 further includes 4 receivers (RX-1 through RX-4) each of whichis selectably coupled to two of the receive antennas 302, providing areconfigurable MIMO system with 8 receive antennas, four of which can beemployed concurrently to collect measurements. Four analog to digitalconverters (ADCs) 306A-306D sample and digitize the down-convertedreceive signals from the receivers RX-1 through RX-4, supplying thedigitized signals to a digital signal processor (DSP) 308 for filteringand processing, or directly to a high-bandwidth interface 310 to enableoff-chip processing of the digitized baseband signals. If used, the DSP308 generates image data that can be conveyed to an ECU via thehigh-bandwidth interface 310.

A control interface 312 enables the ECU or other host processor toconfigure the operation of the transceiver chip 300, including the testand calibration peripheral circuits 314 and the transmit signalgeneration circuitry 304.

FIG. 4 adds additional detail to illustrate the phased-array technique.A transmit signal (for automotive radar, the contemplated frequencyrange is the W band (75 GHz-110 GHz)) is supplied to four programmablephase shifters 402A-402D to provide respective phase shifts to thesignals for each antenna. The adjustable gain amplifiers 303A-303Damplify the phase-shifted signals to drive the transmit antennas, butjust before the drive signals are output from the chips, a set ofcouplers 404A-404D split off a small fraction of the signal power asmonitor signals that enable a calibration circuit 406 to monitor theperformance of the transmit circuitry.

In at least some embodiments, the calibration circuit monitors therelative amplitude and phase of the drive signals. FIG. 5 is a blockdiagram of an illustrative phase detector 502 that may be employed atthe mm-wave frequencies contemplated herein. A quadrature coupler 504converts a local oscillator (LO) signal into two quadrature signals(signals having the same frequency, but out of phase by 90 degrees).Quadrature couplers are known in the literature, and suitable examplesinclude branchline couplers, Lange couplers, and overlay couplers. Asplitter 506 spits an RF input into two equal signals. Multipliers mixeach of the quadrature signals with one of the RF signals to producebaseband voltages. The voltage obtained using the leading quadraturesignal may be termed the in-phase voltage VI, while the voltage obtainedusing the lagging quadrature signal may termed the quadrature-phasevoltage VQ. One or more ADCs 508 may digitize the voltages and aprocessor, ASIC, or look-up table 510 may convert the digitized voltagesinto a detected phase edet by performing the equivalent of an arctangentoperation on the ratio of VQ to VI. The detected phase represents thephase difference between the LO and RF inputs.

FIG. 6 shows an illustrative calibration circuit using a naïve approach,in which the N drive signals are each supplied to a respective RF inputof a phase detector 502A-502N, and the LO inputs of the phase detectorsreceive a buffered copy of the LO signal from a respective amplifier602A-602N. (Even though they impose significant areal requirements, theamplifiers are typically necessary to avoid undue loading of the LOsignal source.) The phase angle measurements from the phase detectors(θ_(i)) indicate the phase angle difference between the LO and RF inputs(with an offset representing contributions from the couplers, theamplifiers, and any routing delay differences):

θ_(i,j)=θ_(RFi)−θ_(ref)=θ_(PSi,j)−θ_(LO)−θ_(offset)

where θ_(PSi,j) is the jth phase shift setting of the ith phase shifter402A-402D, i ranging from 1 to the number of phase shifters and jranging from 1 to the number of programmable phase shifts for each phaseshifter. The operation of each phase shifter can be verified bycomparing the measured phase shifts θ_(i,j) for adjacent values of j andconfirming that the difference matches the expected step change Δθ_(s):

θ_(i,j)−θ_(i,j+1)=Δθ_(s).

The verification may be repeated for each value of j, with wrap-aroundwhen j reaches it maximum value (the number of available phasesettings).

Note that it is also desirable to ensure proper inter-channel phasedifferences. Issues can arise from the distribution of the LO signal toall of the phase detectors, and the phase shift associated with theamplifiers may be temperature dependent. Thus, together with theforegoing step change verification, it is desirable to perform aninter-channel phase difference verification for one or more values of jand k:

θ_(i,j)−θ_(i+1,k)=(j−k)Δθ_(s).

The inter-channel verification may be repeated for each value of i.

FIG. 7 shows an illustrative verification circuit, which replaces theglobal LO signal with use of adjacent channels as the reference LOsignal. The 3-port couplers 404A, 404D at the edges of the array areretained, but the couplers interior to the array (404B, 404C) arereplaced by 4-port couplers 704B, 704C to supply monitor signals to two(rather than one) phase detectors. In at least some embodiments, the4-port couplers consist of a directional coupler cascaded with a powersplitter, while the 3-port couplers may be implemented as standarddirectional couplers.

As before, the couplers split off a small fraction of the RF signalpower, outputting the substantial majority of the signal to therespective transmit antenna. Amplifiers 602A-602C amplify the monitorsignals to drive the LO inputs of the phase detectors 502A-502C. Eachphase detector 502A-502C compares the phases of monitor signals fromadjacent channels. (Because the channels are compared in a pairwisefashion, one fewer phase detector is employed in this arrangement thanin the arrangement of FIG. 6.)

The detected pairwise phase differences θ₁₂, θ₂₃, θ₃₄, are

θ_(i(i+1),jk)=θ_(RF(i+1),k)−θ_(RF,j)−θ_(offset)=θ_(PS(i+1),k)−θ_(PSi,j)−θ_(offset)

As before, the operation of each phase shifter can be verified bycomparing the measured phase shifts for adjacent values of j or k andconfirming that the difference matches the expected step change Des:

θ_(i(i+1),jk)−θ_(i(i+1),(j+1)k)=Δθ_(s)

θ_(i(i+1),jk)−θ_(i(i+1),j(k+1))=Δθ_(s)

The verification may be repeated for each value of j or each value of k,with wrap-around when j or k reaches its maximum value (the number ofavailable phase settings).

For inter-channel phase difference verification, the difference betweenpairwise differences may be used (representing the phase settings ofchannels i, i+1, and i+2 as j, k, and l):

θ_(i(i+1),jk)−θ_((i+1)(i+2),kl)=θ_(PSi,j)+θ_(PS(i+2),l)−2θ_(PS(i+1),k)=(j+l−2k)Δθ_(s).

The inter-channel verification may be repeated for each value of i, withwrap-around as i+1 and i+2 exceed the maximum value (the number ofchannels).

The intra-channel phase shift verification requires a sweep of the phaseshift settings, and as such, is preferably performed between regulartransmissions and as infrequently as is consistent with maintainingconfidence in the proper operation of the radar system. It is expectedthat there may be insufficient opportunity to complete a full sweep inthe time available between regular transmissions, and if that is thecase, the sweep may be performed in stages and spread over multiplemeasurement cycles.

Conversely, the inter-channel phase shift verification does not requirealteration of the phase shifter settings, and accordingly, can beperformed during normal usage. If desired, the inter-channelverification can be performed concurrently with each transmission.

Because measurement differences are being used to verify operation ofthe phase shifters, the phase offset is canceled and it is no longernecessary to determine the offset or calibrate its dependence on age andprocess or temperature variation.

Though the arrangement of FIG. 7 enables verification without expresslyrequiring calibration, there may nevertheless be a need to calibrate thephase shifters and amplifiers of each channel to ensure accurate beamsteering. To that end, FIG. 8 shows an illustrative calibrationarrangement. Rather than supplying phase detectors as shown in FIG. 7,the couplers 404A, 704B, 704C, and 404D of FIG. 8 supply signals topower combiners 802A-802C. Combiner 802A combines monitor signals fromcouplers 404A and 704B to provide a combined signal. Combiner 802Bcombines signals from couplers 702B and 702C. Combiner 802C combinessignals from couplers 704C and 404D.

As discussed further below, combiners 802A-802C can be in-phase powercombiners or anti-phase power combiners. The combined signal output fromeach combiner is coupled to a power detector 804A-804C. In at least somecontemplated embodiments, the power detectors rectify the combinedsignals using a diode or other nonlinear element. The power detectorsproduce a voltage indicative of the power of the combiner outputs. Theoutput of detector 804A is labeled as V12, the output of detector 804Bis labeled as V23, and the output of detector 804C is labeled as V34.These voltages are digitized by ADCs 806A-806C and provided to amicrocontroller unit (MCU) logic 808. In other contemplated embodiments,a single ADC is used with a multiplexer to digitize the detectorvoltages.

As shown in FIGS. 9A-9B, the detector output voltages V depend on therelative phase between the combined signals. The graphs each assume thateach of the two signals is coupled to the combiner at a power level of−10 dBm and no insertion loss. The anti-phase combiner output shown inFIG. 9A has a minimum at zero degrees and increases monotonically ineach direction to maxima at +180°.

The in-phase combiner output shown in FIG. 9B has a maximum at zerodegrees, decreasing monotonically to minima at +180°. Examples of ananti-phase combiner may include a rat-race coupler, a magic tee, abranchline coupler, or a Lange coupler. These can also be configured asin-phase couplers, or the in-phase coupler may be implemented as aWilkinson power converter.

The power detector range doesn't have to be very large to correctlydetect the phase setting offset where θ=0. It is only required that itbe monotonic.

Let us denote the power combiner input voltages as x₁=A₁ cos(ωt) andx₂=A₂ cos(ωt+θ). Disregarding insertion loss, the anti-phase powercombiner output voltage is y=(x₁−x₂)/√{square root over (2)} and thein-phase combiner output voltage is y=(x₁+x₂)/√{square root over (2)}.If one or the other of the phase shifters associated with the inputs tothe combiner are varied, the magnitude of y varies as a function oftheir relative phase angle θ. If A₁=A₂ then y will be zero or willachieve a maximum when the relative phase angle is zero.

We now discuss methods of using the verification circuit of FIG. 7 withreference to FIG. 10A. In block 902, a controller (such as DSP 308)systematically varies the settings of the phase shifters 402A-402D, tosweep the phase of each channel relative to that of its adjacent channelfeeding into one of the phase detectors 502A-502C in FIG. 7. Thisenables the controller to verify that each adjustment of the phasesetting produces a change in the phase detector output corresponding toan expected step change. If this verification is not successful, theprocess halts with an alert to the ECU that a fault exists in the radarsystem. (The controller may transmit an error code to the ECU, set themeasurement to a value indicating an erroneous measurement, and/or set afield in a status register that is periodically read by the ECU.)

Otherwise, in block 904, normal operation begins with the first of aseries of periodic transmit pulses. The controller sets the phaseshifters to the desired setting for steering the beam from the phasedtransmit array in a desired direction, and generates the pulse. As thepulse is generated, the verification circuit measures the relativeinter-channel phases in block 906 as discussed previously, andcalculates differences between adjacent ones of the relativeinter-channel phases, verifying that the difference matches an expecteddifference. If this verification is not successful, the process may haltwith an alert to the ECU that a fault exists in the radar system.

Otherwise, in block 908, the controller collects radar echomeasurements, and blocks 904-908 are repeated to collect a series ofmeasurements. The echo measurements are processed in accordance withexisting practice to determine directions and distances of obstaclesrelative to the vehicle.

We now discuss methods of using the calibration circuit of FIG. 8 withreference to FIG. 10B. In block 910, a controller (such as DSP 308)measures the output level of each channel. In one contemplated approach,the controller enables only one power amplifier 303A-303D for eachadjacent channel. For example, power amplifiers 303A and 303C may beenabled while power amplifiers 303B and 303D are disabled. Subsequently,power amplifiers 303A and 303C may be disabled while amplifiers 303B and303D are enabled. The disabled power amplifiers provide no outputsignal.

While only one power amplifier is enabled for each pair of adjacentchannels, the controller measures the output of power detectors804A-804C. The process is repeated with the other power amplifierenabled for each pair of adjacent channels, providing the controllerwith a power level measurement for each channel. The controller may thenequalize the power levels in block 912 by adjusting the power amplifiersetting, e.g., raising the amplifier setting for the channel with thelowest power level and/or lowering the amplifier setting for the channelwith the highest power level. The controller performs a verificationstep, repeating the operations of blocks 910 and 912 until the powerlevels are equal.

Once the power levels have been equalized, the controller performs phasecalibration, beginning in block 914. The controller sweeps the settingof a phase shifter while holding the setting of the phase shifter on theadjacent channel constant. When the detected power level reaches aminimum (for anti-phase combiners) or a maximum (for in-phasecombiners), the controller notes the relative phase shifter settings(i.e., the phase setting offset) and in block 916 designates that phasesetting offset as a relative phase angle θ=0, such that desired phasedifferences may be achieved by suitably increasing or decreasing therelative phase shifter settings with reference to the phase settingoffset. The process is performed for each pair of adjacent channels, andmay be verified for all phase shift settings of each phase shifter.

Thereafter, during normal operations represented by blocks 918-922, thecontroller sets the phase shifters to the desired setting for steeringthe beam from the phased transmit array in a desired direction, andgenerates the pulse. As the pulse is generated, the verification circuitmeasures the power detector output levels in block 920 and verifies thatthey match the power output level expected for the desired phase shift(see FIGS. 9A-9B). If this verification is not successful, the processmay halt with an alert to the ECU that a fault exists in the radarsystem.

Otherwise, in block 922, the controller collects radar echomeasurements, and blocks 918-922 are repeated to collect a series ofmeasurements. The echo measurements are processed in accordance withexisting practice to determine directions and distances of obstaclesrelative to the vehicle.

It is noted that the implementation of FIG. 8 may require a much smallersilicon area since the RF signals are converted to baseband/DC using apower detector instead of a down-converting I/O mixer. Both embodimentsavoid routing of long lines to a calibration receiver which, wheninterleaved with the RF lines that carry the TX signals, may reducefidelity. The coupled RF signals are converted to DC immediately and arethus much easier to route.

Numerous other modifications, equivalents, and alternatives, will becomeapparent to those of ordinary skill in the art once the above disclosureis fully appreciated. For example each of the disclosed circuitarrangements may be used for verification or for calibration or both. Itis intended that the following claims be interpreted to embrace all suchmodifications, equivalents, and alternatives where applicable.

What is claimed is:
 1. A method that comprises: programming a set ofphase shifters to convert a radio frequency signal into a set of channelsignals; splitting off a monitor signal from each channel signal whilecoupling the set of channel signals to a set of antenna feeds; and whiletaking the monitor signals in pairs associated with adjacent channels,measuring a relative phase between each pair of monitor signals.
 2. Themethod of claim 1, further comprising providing an error notification ifone of said relative phase measurements fails to match a difference inprogrammed phase shifts of the set of phase shifters.
 3. The method ofclaim 1, further comprising: acquiring sequential relative phasemeasurements over a range of phase settings of phase shifters associatedwith even channels while maintaining a phase setting of phase shiftersassociated with odd channels; acquiring sequential relative phasemeasurements over a range of phase settings of phase shifters associatedwith odd channels while maintaining a phase setting of phase shiftersassociated with even channels; and providing an error notification if adifference between sequential relative phase measurements fails to matcha predetermined step size.
 4. The method of claim 1, further comprisingdetermining a phase setting offset for each pair based on the relativephase measurements.
 5. The method of claim 4, wherein said determiningincludes measuring the relative phase over a range of phase settingdifferences for adjacent channels.
 6. The method of claim 1, whereinsaid measuring includes: combining each pair of monitor signals to forma combined signal; and measuring a power of each combined signal.
 7. Themethod of claim 6, further comprising: disabling adjustable gainamplifiers associated with odd channels while measuring the power ofeach combined signal; disabling adjustable gain amplifiers associatedwith even channels while measuring the power of each combined signal;and based on said power measurements, adjusting gains of the adjustablegain amplifiers to equalize the power of each channel signal in said setof channel signals.
 8. A radar system that comprises: a signal generatorthat supplies a radio frequency signal; a set of programmable phaseshifters that convert the radio frequency signal into a set of channelsignals; a set of couplers that couples the set of channel signals to aset of antenna feeds, the couplers in said set providing monitorsignals; one or more power combiners that each combine a pair of monitorsignals to produce a combined signal; one or more power detectors thateach convert a respective combined signal into a power level signal; anda controller that uses at least one said power level signal to determinea relative phase between at least one pair of channel signals in saidset of channel signals.
 9. The system of claim 8, wherein the controlleruses the at least one power level signal to determine a phase settingoffset for each pair.
 10. The method of claim 9, wherein the controllerdetermines the phase setting offset includes: measuring the at least onepower level signal over a range of phase setting differences foradjacent channels; and identifying a power level maximum or minimum thatcorresponds to the phase setting offset.
 11. The method of claim 10,wherein the one or more power combiners are anti-phase combiners and thephase setting offset corresponds to a power level minimum.
 12. Themethod of claim 10, wherein the one or more power combiners are in-phasecombiners and the phase setting offset corresponds to a power levelmaximum.
 13. The system of claim 8, further comprising: a set ofadjustable gain amplifiers that amplify the set of channel signalsprovided to the set of couplers.
 14. The system of claim 13, whereinprior to determining the relative phase, the controller adjusts gains ofthe adjustable gain amplifiers to equalize power of each channel signalin the set of channel signals.
 15. The system of claim 14, wherein priorto equalizing power, the controller: disables the adjustable gainamplifiers associated with odd channels while measuring the power ofeach combined signal; and disables the adjustable gain amplifiersassociated with even channels while measuring the power of each combinedsignal.
 16. A radar system that comprises: a signal generator thatsupplies a radio frequency signal; a set of programmable phase shiftersthat convert the radio frequency signal into a set of channel signals; aset of couplers that couples the set of channel signals to a set ofantenna feeds, the couplers in said set providing monitor signals; andone or more phase detectors that each determine a relative phase betweenmonitor signals for a pair of adjacent channels.
 17. The radar system ofclaim 16, further comprising a controller that: acquires sequentialrelative phase measurements over a range of phase settings of phaseshifters associated with even channels while maintaining a phase settingof phase shifters associated with odd channels; acquires sequentialrelative phase measurements over a range of phase settings of phaseshifters associated with odd channels while maintaining a phase settingof phase shifters associated with even channels; and provides an errornotification if a difference between sequential relative phasemeasurements fails to match a predetermined step size.
 18. The radarsystem of claim 16, wherein the one or more phase detectors comprises apair of phase detectors that determines a first relative phase between acenter channel and a first adjacent channel, and a second relative phasebetween the center channel and a second adjacent channel, the systemfurther comprising a controller that computes a difference between thefirst and second relative phases.
 19. The radar system of claim 18,wherein the controller provides an error notification if the differencefails to match an expected difference based on phase settings of thephase shifters associated with the center channel, the first adjacentchannel, and the second adjacent channel.
 20. The radar system of claim19, wherein the expected difference is (j+l−2k)Δθ_(s), with j, k, and lrepresenting phase settings of the first adjacent channel, the centerchannel, and the second adjacent channel, respectively, and Δθ_(s)representing a predetermined step change.